Emulsifier-free finely disperse systems of the oil-in-water and water-in-oil type

ABSTRACT

Pickering emulsions, which are finely disperse systems of the water-in-oil or oil-in-water type, comprising 
     (1) an oil phase, 
     (2) a water phase, 
     (3) at least one type of microfine particles which 
     a) have an average particle size of less than 200 nm, which 
     b) display both hydrophilic and lipophilic properties, and are dispersible both in water and in oil and which 
     c) have optionally been coated on the surface, 
     (4) at least one electrolyte and 
     (5) at most 0.5% by weight of one or more emulsifiers.

DESCRIPTION

Emulsifier-free finely disperse systems of the oil-in-water andwater-in-oil type

The present invention relates to emulsifier-free finely disperse systemsof the oil-in-water and water-in-oil type, preferably as cosmetic ordermatological preparations.

Emulsions are generally taken to mean heterogeneous systems whichconsist of two liquids which are immiscible or have only limitedmiscibility with one another, which are usually referred to as phases.In an emulsion, one of the two liquids is dispersed in the form of veryfine droplets in the other liquid.

If the two liquids are water and oil and if oil droplets are finelydispersed in water, then this is an oil-in-water emulsion (O/W emulsion,e.g. milk). The basic character of an O/W emulsion is defined by thewater. In a water-in-oil emulsion (W/O emulsion, e.g. butter), theprinciple is reversed, the basic character here being determined by theoil.

In order to achieve permanent dispersion of one liquid in another,emulsions in the traditional sense require the addition of aninterface-active substance (emulsifier). Emulsifiers have an amphiphilicmolecular structure, consisting of a polar (hydrophilic) and a nonpolar(lipophilic) molecular moiety, which are spatially separate from oneanother. In simple emulsions, finely disperse droplets of one phase,surrounded by an emulsifier shell, (water droplets in W/O emulsions orlipid vesicles in O/W emulsions) are present in the second phase.Emulsifiers lower the interfacial tension between the phases bypositioning themselves at the interface between two liquids. At thephase boundary, they form oil/water interfacial films, which preventirreversible coalescence of the droplets. Emulsions are frequentlystabilized using emulsifier mixtures.

Traditional emulsifiers can, depending on their hydrophilic molecularmoiety, be divided into ionic (anionic, cationic and amphoteric) andnonionic:

The most well-known example of an anionic emulsifier is soap, which isusually the term used for the water-soluble sodium or potassium salts ofsaturated or unsaturated higher fatty acids.

Important examples of cationic emulsifiers are quaternary ammoniumcompounds.

The hydrophilic molecular moiety of nonionic emulsifiers frequentlyconsists of glycerol, polyglycerol, sorbitans, carbohydrates andpolyoxyethylene glycols, and, in most cases, is linked to the lipophilicmolecular moiety via ester and ether bonds. The lipophilic molecularmoiety usually consists of fatty alcohols, fatty acids or isofattyacids.

By varying the structure and the size of the polar and nonpolarmolecular moiety, the lipo-philicity and hydrophilicity of emulsifierscan be varied within wide limits.

A decisive factor for the stability of an emulsion is the correct choiceof emulsifiers. The characteristics of all substances present in thesystem are to be taken into consideration here. In the case of, forexample, skincare emulsions, polar oil components and, for example, UVfilters lead to instability. As well as the emulsifiers, therefore,other stabilizers are also used which, for example, increase theviscosity of the emulsion and/or act as protective colloid.

Emulsions are an important type of product in the field of cosmeticand/or dermatological preparations.

Cosmetic preparations are essentially used for skin care. The main aimof skin care in the cosmetics sense is to strengthen or rebuild theskin's natural function as a barrier against environmental influences(e.g. dirt, chemicals, microorganisms) and against the loss ofendogenous substances (e.g. water, natural fats, electrolytes). If thisfunction becomes impaired, increased resorption of toxic or allergenicsubstances or attack by microorganisms may result, leading to toxic orallergic skin reactions.

Another aim of skin care is to compensate for the loss by the skin oflipids and water caused by daily washing. This is particularly importantif the natural regeneration ability is inadequate. Furthermore, skincareproducts should protect against environmental influences, in particularagainst sun and wind, and delay skin ageing.

Cosmetic preparations are also used as deodorants. Such formulations areused to control body odour, which is produced when fresh perspiration,which is in itself odourless, is decomposed by microorganisms.

Medicinal topical compositions usually comprise one or more medicamentsin an effective concentration. For the sake of simplicity, in order todistinguish clearly between cosmetic and medicinal use and correspondingproducts, reference is made to the legal provisions in the FederalRepublic of Germany (e.g. Cosmetics Directive, Foods and Drugs Act).

The use of customary emulsifiers in cosmetic or dermatologicalpreparations is in itself acceptable. Nevertheless, emulsifiers, likeultimately any chemical substance, may in certain circumstances causeallergic reactions or reactions based on oversensitivity of the user.

For example, it is known that certain light dermatoses are triggered bycertain emulsifiers, but also by various fats and simultaneous exposureto sunlight. Such light dermatoses are also called “Mallorca acne”.There has thus been no lack of attempts to reduce the amount ofcustomary emulsifiers to a minimum, in the ideal case even to zero.

A reduction in the required amount of emulsifier can, for example, beachieved by taking advantage of the fact that very finely divided solidparticles have an additional stabilizing action. The solid substanceaccumulates at the oil/water phase boundary in the form of a layer, as aresult of which coalescence of the disperse phases is prevented. It isnot the chemical properties of the solid particles which are offundamental importance here, but the surface properties.

Around 1910, Pickering prepared paraffin/water emulsions which werestabilized merely by the addition of various solids, such as basiccopper sulphate, basic iron sulphate or other metal sulphates. This typeof emulsion is thus also referred to as a Pickering emulsion.

The original forms of Pickering emulsions initially surfaced, as itwere, as undesired secondary effects in a variety of industrialprocesses, such as, for example, in secondary oil recovery, theextraction of bitumen from tar sand and other separation processesinvolving two immiscible liquids and fine, dispersed solid particles.These are generally W/O emulsions which are stabilized by mineralsolids. Accordingly, investigation of corresponding systems, such as,for example, the oil/water/soot or oil/water/slate dust systems wasinitially the focus of research activity.

Basic experiments have shown that one characteristic of a Pickeringemulsion is that the solid particles are arranged at the interfacebetween the two liquid phases, where they form, as it were, a mechanicalbarrier against the combining of the liquid droplets.

It is a relatively new technical development to use Pickering emulsionsas a base for cosmetic or dermatological preparations.

One way of achieving solids stabilization in the sense of a pickeringemulsion in a cosmetic or dermatological preparation is, according toMay-Alert (Pharmazie in unserer Zeit [Pharmacy in our time], Vol. 15,1986, No. 1, 1-7) for example, to use emulsifier mixtures which compriseboth anionic and cationic surfactants. Since mixing anionic and cationicsurfactants always results in the precipitation of insoluble,electroneutral compounds, deliberate precipitation of these neutralsurfactants in the oil/water interface makes it possible to achieveadditional solids stabilization.

European Laid-open Specification 0 686 391, moreover, describesemulsions of the water-in-oil type which are free from surface-activesubstances and are stabilized only by solids. Stabilization is achievedhere using spherical polyalkylsilsesquioxane particles which have adiameter of from 100 nm up to 20 μm. These emulsions can be referred toas Pickering emulsions according to that mentioned above.

Pickering emulsions are stabilized by the use of suitable solids orpigments. However, the preparations of the prior art generally have thedisadvantage that they are limited to a narrow field of application or arestricted choice of starting materials since they can only be stablyformulated in this manner. For many areas of cosmetics (e.g. for thefield of face care), Pickering emulsions of the prior art haveunsatisfactory cosmetic properties.

The object was therefore to remedy the disadvantages of the prior art.In particular, the intention was to provide cosmetic and dermatologicalbases for cosmetic and dermatological preparations which arecharacterized by good skin tolerability.

In addition, an object of the present invention was to provide productswith the widest possible variety of applications. For example, theintention was to provide bases for preparation forms such as cleansingemulsions, facecare and bodycare preparations or deodorants, but alsodistinctly medicinal-pharmaceutical presentations, for examplepreparations against acne and other skin conditions.

It was surprising and in no way predictable by the person skilled in theart that Pickering emulsions, which are finely disperse systems of thewater-in-oil or oil-in-water type, comprising

(1) an oil phase,

(2) a water phase,

(3) at least one type of microfine particles which

a) have an average particle size of less than 200 nm, which

b) display both hydrophilic and lipophilic properties, i.e. which haveamphiphilic character, and are dispersible both in water and in oil andwhich

c) have optionally been coated on the surface,

(4) at least one electrolyte and

(5) at most 0.5% by weight of one or more emulsifiers, overcome thedisadvantages of the prior art.

According to the invention, it is particularly advantageous if thepreparations comprise significantly less than 0.5% by weight of one ormore emulsifiers or are even entirely free from emulsifiers.

The preparations according to the invention are extremely satisfactorypreparations in every respect which have considerably higher stabilitycompared with traditional Pickering emulsions and are therefore suitablein particular to serve as bases for preparation forms having diverseapplication purposes. In particular, W/O Pickering emulsions within themeaning of the present invention are, surprisingly, markedly stable.

In addition, the preparations according to the invention arecharacterized by excellent skin tolerability. In addition, it wassurprising that preparations according to the invention, which are inthe form of a sunscreen, exhibit higher effectiveness than customarysunscreen formulations.

While preparations of the prior art having a pigment content of aslittle as 1% by weight produce a dull feel following their applicationto the skin, which increases further with higher pigment concentrations,the preparations according to the invention, surprisingly, do not leavea dry or dull impression on the skin, but on the contrary exhibitexcellent cosmetic properties.

Although the prior art recognizes, in addition to Pickering emulsions,emulsifier-free, finely disperse cosmetic or dermatologicalpreparations, which are generally referred to as hydrodispersions andwhich are dispersions of a liquid, semisolid or solid inner(discontinuous) lipid phase in an outer aqueous (continuous) phase, theprior art was unable to point the way to the present invention.

In the case of hydrodispersions of a liquid lipid phase in an externalaqueous phase, the stability can be guaranteed, for example, by buildingup a gel structure in the aqueous phase, in which the lipid droplets arestably suspended.

German Laid-Open specification 44 25 268 describes stable finelydisperse, emulsifier-free cosmetic or dermatological preparations of theoil-in-water type, which in addition to an oil and a water phase containone or more thickeners from the group consisting of the acrylic acidpolymers, polysaccharides and their alkyl ethers, where a lowering ofinterfacial tension must not be measurable for these thickeners.

Based on similar hydrodispersions, German Laid-Open specification 43 03983 discloses cosmetic or dermatological sunscreen formulations whichare essentially free of emulsifiers, the hydrodispersion of inorganicmicropigments which serve as UV filter substances being incorporatedinto the lipid phase.

O/W Pickering emulsions within the meaning of the present invention,however, are obtainable by first dispersing amphiphilic particlesaccording to the invention which are suitable for the preparation of O/WPickering emulsions in the water phase and then combining the waterphase with the fatty phase. W/O Pickering emulsions according to theinvention, however, are obtainable by dispersing amphiphilic particlesaccording to the invention which are suitable for the preparation of W/OPickering emulsions in the fatty phase.

According to the invention, the electrolyte(s) is/are advanatgeouslyselected from the group consisting of

(1) the salts with the following anions: chlorides, furthermoreinorganic oxo element anions, of these in particular sulphates,carbonates, phosphates, borates and aluminates. Electrolytes based onorganic anions are also advantageous, e.g. lactates, acetates,benzoates, propionates, tartrates, citrates, amino acids and their saltsand many others. Comparable effects can also be achieved by means ofethylenediaminetetraacetic acid and its salts.

Cations of the salts preferably used are ammonium, alkylammonium, alkalimetal, alkaline earth metal, magnesium, iron and zinc ions. It does notneed mentioning per se that only physiologically acceptable electrolytesshould be used in cosmetics. Potassium chloride, sodium chloride,magnesium sulphate, zinc sulphate and mixtures thereof are particularlypreferred.

According to the invention, the electrolyte(s) is/are furthermoreadvantageously selected from the group (2), which comprises:

(2) certain water-soluble UV filter substances which are mostly presentas alkali metal salts, in particular those which carry one or moresulphonic acid groups or sulphonate groups in their molecular structure:

2-phenylbenzimidazole-5-sulphonic acid and its salts, for example thesodium or potassium salt or its triphenolammonium salt

 sulphonic acid derivatives of benzophenones, preferably2-hydroxy-4-methoxybenzophenone-5-sulphonic acid and its salts, forexample the corresponding sodium, potassium or triphenolammonium salt:

 sulphonic acid derivatives of 3-benzylidenecamphor, such as, forexample, 4-(2-oxo-3-bornylidenemethyl)benzenesulphonic acid and itssalts, for example the corresponding sodium, potassium ortriethanolammonium salt:

 2-methyl-5-(2-oxo-3-bornylidenemethyl)benzenesulphonic acid and itssalts, for example the corresponding sodium, potassium ortriethanolammonium salt:

 1,4-di(2-oxo-10-sulpho-3-bornylidenemethyl)benzene and its salts (thecorresponding 10-sulphato compounds, for example the correspondingsodium, potassium or triethanolammonium salt), also referred to asbenzene-1,4-di(2-oxo-3-bornylidenemethyl-10-sulphonic acid:

According to the invention, the electrolyte(s) is/are furthermoreadvantageously selected from the group consisting of

(3) the amino acids and their salts or their anions. Amino acids are aconstituent of the natural moisturizing factor. The addition of aminoacids, in particular of essential amino acids, is to be regarded asadvantageous, since moisture can be bound up in the skin by means ofhydration processes.

Amino acids having a particularly advantageous cosmetic ordermatological action are glycine, alanine, valine, leucine, isoleucine,phenylalanine, tyrosine, proline, hydroxyproline, serine, threonine,cysteine, methionine, tryptophan and arginine.

According to the invention, the electrolyte(s) is/are furtheradvantageously selected from the group consisting of

(4) the cosmetically and dermatologically relevant α-hydroxycarboxylicacids, α-ketocarboxylic acids and β-hydroxycarboxylic acids and inparticular their salts, where the cations can advantageously be selectedfrom the group consisting of ammonium, alkylammonium, alkali metal,alkaline earth metal, magnesium, iron and zinc ions.

α-Hydroxycarboxylic acids which are cosmetically or dermatologicallyrelevant obey the general formula

 β-Hydroxycarboxylic acids which are cosmetically or dermatologicallyrelevant obey the general formula

 α-Ketocarboxylic acids which are cosmetically or dermatologicallyrelevant obey the general formula

 where in each case R′ and R″ independently of one another are selectedfrom the groups

(a1) H,

(a2) branched or unbranched C₁₋₂₅-alkyl,

(a3) branched or unbranched C₁₋₂₅-alkyl substituted by one or morecarboxyl groups and/or hydroxyl groups and/or aldehyde groups and/or oxogroups (keto groups),

(a4) phenyl,

(a5) phenyl substituted by one or more carboxyl groups and/or hydroxylgroups and/or branched and/or unbranched C₁₋₂₅-alkyl groups, or wherethe α-carbon atom and the β-carbon atom of the β-hydroxycarboxylic acidwith R′ and R″ together form an

(a6) unsubstituted cycloalkyl group or aryl group having 3 to 7 ringatoms or a

(a7) cycloalkyl group or aryl group having 3 to 7 ring atoms substitutedby one or more carboxyl groups and/or hydroxyl groups and/or oxo groups(keto groups) and/or branched and/or unbranched C₁₋₂₅-alkyl groups and

where the α-hydroxycarboxylic acids or the β-hydroxycarboxylic acids orthe α-ketocarboxylic acids can optionally be present in the form oftheir physiologically tolerable salts.

α-Hydroxycarboxylic acids, β-hydroxycarboxylic acids andα-ketocarboxylic acids advantageously to be used in the context of thepresent invention follow, these also being mentioned as representingtheir salts or anions:

salicylic acid (also 2-hydroxybenzoic acid), which is characterized bythe structure

As is known, salicylic acid has an antibacterial and keratolytic actionand is a constituent of some cosmetic or pharmaceutical preparations.

The α-hydroxycarboxylic acids according to the invention areadvantageously selected from the following substance classes:

(b1) α-hydroxy fatty acids, these in turn being particularlyadvantageously selected from the group consisting of theC₁₀₋₁₈-alkylcarboxylic acids,

(b2) α-hydroxy sugar acids, aliphatic α-hydroxy fruit acids,

(b3) unsubstituted aromatic α-hydroxycarboxylic acids (e.g. madelicacid) and

(b4) substituted aromatic α-hydroxycarboxylic acids.

The α-hydroxy fatty acids coming under (b1) are particularlyadvantageously selected from the group consisting of

where n in each case is a number smaller than 7.

It is furthermore advantageous to use mixtures of such aliphaticα-hydroxycarboxylic acids, in particular in the form of wool wax acidmixtures in which the content of α-hydroxycarboxylic acids is 20 to 30%by weight, based on the total composition.

The α-hydroxy sugar acids coming under item (b2) are particularlyadvantageously selected from the group consisting of the

aldonic acids, e.g. gluconic acid, galactonic acid

aldaric acids, e.g. glucaric acid, galactaric acid (but also the fruitacid tartaric acid, which likewise comes under the definition of aldaricacid)

uronic acids, e.g. glucuronic acid, galacturonic acid

glyceric acid

The aliphatic α-hydroxy fruit acids coming under item (b2) areparticularly advantageously selected from the group consisting of malicacid, lactic acid, citric acid and tartaric acid.

Malic acid (hydroxysuccinic acid) is characterized by the followingchemical struture:

Lactic acid (2-hydroxypropanoic acid) is characterized by the followingchemical structure:

Citric acid (2-hydroxy-1,2,3-propanetricarboxylic acid) is characterizedby the following chemical structure:

As is known, citric acid is used for buffering cosmetic and/ordermatological preparations, but also as a synergist for antioxidants inskin and hair cosmetics.

Tartaric acid (dihydroxysuccinic acid) is characterized by the followingchemical structure:

The preferred α-ketocarboxylic acid is pyruvic acid (α-oxypropanoicacid). It is distinguished by the following structure:

The total amount of one or more electrolytes in the finished cosmetic ordermatological preparations is advantageously selected to be less than5% by weight, preferably between 0.5 and 2.0% by weight, based on thetotal weight of the preparations.

It is particularly preferred within the meaning of the present inventionto stabilize W/O Pickering emulsions by the addition of electrolytesaccording to the invention.

It is also advantageous, although not obligatory, for the Pickeringemulsions according to the invention to comprise other auxiliaries whichcan additionally increase the stability of these preparations, forexample substances which are chosen from the group of waxes and/or oilthickeners, and of hydrocolloids.

It is also advantageous for the Pickering emulsions according to theinvention to comprise auxiliaries which can contribute to reducing orpreventing a dull or dry feel on the skin following their application,where it is possible that the main purpose of these substances is adifferent one. Preferably, these substances are, for example, chosenfrom the group of unsymmetrically substituted s-triazine derivatives,cyclodextrins, film formers and polymeric moisturizers, it beingpossible for these substances to be present either individually or in amixture.

The cosmetic properties of the Pickering emulsions according to theinvention can additionally, for example, be further improved by alsousing oils in the oil phase which have a viscosity of less than 30mPa.s, in particular of less than 20 mPa.s (determined using a rheometerfrom Contraves (Rheomat 108E) at a shear gradient of 500/s and atemperature of 25° C.).

Microfine Particles

The amphiphilic character of the microfine particles according to theinvention is evident, for example, from the fact that they aredispersible both in water and in oil.

It is advantageous to choose the average particle diameter of theparticles used to be between 1 nm and 200 nm, particularlyadvantageously between 5 nm and 100 nm.

It is also advantageous to choose the concentration of all amphiphilicparticles according to the invention to be greater than 0.1% by weight,particularly advantageously between 0.1% by weight and 30% by weight,based on the total weight of the preparations.

For the purposes of the present invention, advantageous particles areall those which are suitable for stabilizing Pickering W/O emulsions orPickering O/W emulsions. It is essentially insignificant for the presentinvention in which of the potentially naturally occurring modificationsthe particles are present.

To stabilize the Pickering emulsions, preference is given to usinguntreated, virtually pure pigment particles, in particular those whichcan be used as dyes in the food industry and/or as absorbers of UVradiation in sunscreens. Examples of advantageous pigments are the zincoxide pigments available from Merck which are available under the tradenames Zinkoxid neutral from Haarmann & Reimer or NanoX from HarcrosChemical Group.

For the purposes of the present invention, Pickering emulsions arelikewise advantageously stabilized by inorganic pigments which have beensurface-treated (“coated”) to repel water, where at the same time theintention is to form or retain the amphiphilic character. Thissurface-treatment can consist in providing the pigments with a thinhydrophobic layer by processes known per se.

One such process, which is described below using titanium dioxide as anexample, consists in, for example, producing the hydrophobic surfacelayer according to the following reaction

nTiO₂ +m(RO)₃Si—R′→nTiO₂ (surf.).

n and m are arbitrary stoichiometric parameters, and R and R′ are thedesired organic radicals. Particularly advantageous are TiO₂ pigments,for example those coated with aluminium stearate, available under thetrade name MT 100 T from TAYCA.

A further advantageous coating of the inorganic pigments consists ofdimethylpolysiloxane (also: dimethicone), a mixture of completelymethylated, linear siloxane polymers which are terminally blocked withtrimethylsiloxy units. For the purposes of the present invention,particularly advantageous pigments are zinc oxide pigments which arecoated in this way.

Also advantageous is a coating of the inorganic pigments with a mixtureof dimethylpolysiloxane, in particular dimethylpolysiloxane having anaverage chain length of from 200 to 350 dimethylsiloxane units, andsilica gel, which is also referred to as simethicone. It is particularlyadvantageous if the inorganic pigments have been additionally coatedwith aluminium hydroxide or hydrated aluminium oxide (also: alumina, CASNo.: 1333-84-2). Particularly advantageous are titanium dioxides whichhave been coated with simethicone and alumina, it being possible for thecoating to also comprise water. One example thereof is the titaniumdioxide available under the trade name Eusolex T2000 from Merck.

For the purposes of the present invention it is also advantageous to usea mixture of different pigment types either within a crystal, forexample as mixed iron oxide, or by combination of two or more pigmenttypes within a preparation.

The Pickering emulsions are also preferably stabilized by boron nitrideparticles, for example by the boron nitrides listed below:

Trade name Available from Boron Nitride Powder Advanced Ceramics BoronNitride Powder Sintec Keramik Ceram Blanche Kawasaki HCST Boron NitrideStark Tr{dot over (e)}s BN ® Carborundum Wacker-Bornitrid BNPWacker-Chemie

It is advantageous to choose the average particle diameter of the boronnitride particles used to be less than 20 μm, particularlyadvantageously less than 15 μm. For the purposes of the presentinvention, Pickering emulsions are likewise advantageously stabilized byboron nitride particles which have been surface-treated (“coated”) torepel water, where at the same time the intention is to form or retainthe amphiphilic character.

An advantageous coating of the boron nitride particles consists ofdimethylpolysiloxane (dimethicone). The boron nitride particles treatedwith dimethicone and available from Carborundum under the trade nameTrès BN® UHP 1106 are advantageous, for example.

Also advantageous is a coating of the boron nitride particles withpolymethylhydrogensiloxane, a linear polysiloxane which is also referredto as methicone. Advantageous boron nitride particles treated withmethicone are, for example, those available from Carborundum under thetrade name Très BN® UHP 1107.

It is also advantageous to stabilize the Pickering emulsions accordingto the invention using microfine polymer particles.

For the purposes of the present invention, examples of advantageousmicrofine polymer particles are polycarbonates, polyethers,polyethylenes, polypropylenes, polyvinyl chloride, polystyrene,polyamides, polyacrylates and the like.

Advantageous according to the invention are, for example, microfinepolyamide particles which are available under the trade name SP-500 fromTORAY. Also advantageous are polyamide 6 (also: nylon 6) and polyamide12 (also: nylon 12) particles. Polyamide 6 is the polyamide formed fromε-aminocaproic acid (6-aminohexanoic acid) or ε-caprolactam[poly(ε-caprolactam)], and polyamide 12 is a poly(ε-laurolactam) fromε-laurolactam. For the purposes of the present invention, Orgasol® 1002(polyamide 6) and Orgasol® 2002 (polyamide 12) from ELF ATOCHEM, forexample, are advantageous.

Other advantageous polymer particles are microfine polymethacrylates.Such particles are available, for example, under the trade namePOLYTRAP® from DOW CHEMICAL.

It is particularly advantageous, but not obligatory, if the microfinepolymer particles used have been surface-coated. This surface-treatmentcan consist in providing the pigments with a thin hydrophilic layer byprocesses known per se. Advantageous coatings consist, for example, ofTiO₂, ZrO₂ or also other polymers, such as, for example, polymethylmethacrylate.

Particularly advantageous microfine polymer particles for the purposesof the present invention are also obtainable by the process, describedin U.S. Pat. No. Specification 4,898,913, for the hydrophilic coating ofhydrophobic polymer particles.

It is advantageous to choose the average particle diameter of themicrofine polymer particles used to be less than 100 μm, particularlyadvantageously less than 50 μm. In this connection, it is essentiallyinsignificant in which form (platelets, rods, spherules, etc.) thepolymer particles used are present.

In addition, it is advantageous to stabilize the Pickering emulsionsaccording to the invention using modified polysaccharides.

For the purposes of the present invention, modified polysaccharides are,for example, obtainable by reaction of starch with mono-, bi- orpolyfunctional reagents or oxidizing agents in reactions which proceedin a largely polymer-analogous manner.

Such reactions are based essentially on modifications of the hydroxylgroups of the polyglucans by etherification, esterification or selectiveoxidation. This produces, for example, so-called starch ethers andstarch esters of the general structural formula

in which R can, for example, be a hydrogen and/or an alkyl and/or anaralkyl radical (in the case of starch ethers) or a hydrogen and/or anorganic and/or inorganic acid radical (in the case of starch esters).Starch ethers and starch esters are advantageous, modifiedpolysaccharides for the purposes of the present invention.

Particularly advantageous starch ethers are, for example, those whichare obtainable by etherification of starch withtetramethylolacetylenediurea and which are referred to asnon-mucilaginous starch (nonswelling starch).

Also particularly advantageous are starch esters and salts thereof, forexample the sodium and/or aluminium salts of half-esters of starch whichhave low degrees of substitution, in particular sodium starch n-octenylsuccinate of the structural formula (II) in which R is characterized bythe following structure

and which is available, for example, under the trade name Amiogum® 23from CERESTAR, and aluminium starch octenyl succinates, in particularthose available under the trade names Dry Flo® Elite LL and Dry Flo® PCfrom CERESTAR.

It is advantageous to choose the average particle diameter of themodified polysaccharide used to be less than 20 μm, particularlyadvantageously less than 15 μm.

The list of given modified polysaccharides which are able to stabilizePickering emulsions according to the invention is of course not intendedto be limiting. For the purposes of the present invention, modifiedpolysaccharides are obtainable in a large number of ways known per se,both of a chemical and a physical nature.

The abovementioned amphiphilic particles are outstandingly suitable bothfor the stabilization of W/O Pickering emulsions and for thestabilization of O/W Pickering emulsions. Microfine particles accordingto the invention which advantageously stabilize one of the two emulsiontypes W/O or O/W in particular are mentioned below.

W/O Pickering Emusions

The water phase proportion of the W/O Pickering emulsions according tothe invention is preferably selected from the range of 0.5 to 75% byweight, based on the total weight of the formulations.

In particular, magnesium silicates (also: talc), for example thoseobtainable under the trade name Talkum Micron from Grolmann are alsoadvantageous for the stabilization of W/O Pickering emulsions.

O/W Pickering Emulsions

The fatty phase proportion of the O/W Pickering emulsions according tothe invention is preferably selected from the range of 0.5 to 75% byweight, based on the total weight of the formulations.

Within the meaning of the present invention, untreated, almost purepigment particles, for example titanium dioxide pigments, in particularthose which are obtainable under the trade name KRONOS® 1171 (TiO₂) fromKronos Titan, are also particularly advantageous for the stabilizationof O/W Pickering emulsions.

Within the meaning of the present invention, O/W Pickering emulsions arefurthermore particularly advantageously stabilized by metal oxideparticles which are coated with aluminium hydroxide and/or silicondioxide. Advantageous embodiments are, for example, titanium dioxideparticles, which are obtainable under the name EUSOLEX® TA from Merck.

It is furthermore advantageous, although not obligatory, to combine themicrofine particles according to the invention with further amphiphilicparticles which can optionally also contribute to the stabilization ofthe Pickering emulsions.

Such particles are, for example, titanium dioxide pigments which arecoated with octylsilanol, and/or silicon dioxide particles which have awater-repellent treatment on the surface. Suitable silicon dioxideparticles are, for example, spherical polyalkylsilsesquioxane particles,such as are mentioned in European Laid-open Specification 0 686 391.Such polyalkyl silsesquioxane particles are obtainable, for example,from Degussa under the trade names Aerosil R972 and Aerosil 200V.Suitable titanium dioxide particles are likewise obtainable from Degussaunder the trade name T805.

The Pickering emulsions according to the invention can be used as a basefor cosmetic or dermatological formulations. These can have thecustomary composition and can serve, for example, for the treatment andthe care of the skin, as a lipcare product, as a deodorant product andas a make-up or make-up removal product in decorative cosmetics or as asunscreen preparation. For use, the cosmetic and dermatologicalpreparations according to the invention are applied to the skin in asufficient amount in the manner customary for cosmetics.

Accordingly, cosmetic or topical dermatological compositions within themeaning of the present invention can be used, depending on theircomposition, for example, as a skin-protection cream, cleansing milk,sunscreen lotion, nutrient cream, day or night cream etc. It isoptionally possible and advantageous to use the compositions accordingto the invention as a base for pharmaceutical formulations.

The cosmetic and dermatological preparations according to the inventioncan contain cosmetic auxiliaries, such as are customarily used in suchpreparations, e.g. preservatives, bactericides, perfumes, substances forpreventing foaming, colourants, pigments which have a colouring action,thickeners, emollient, moisturizing and/or humectant substances, fats,oils, waxes or other customary constituents of a cosmetic ordermatological formulation such as alcohols, polyols, polymers, foamstabilizers, electrolytes, organic solvents or silicone derivatives.

Pickering emulsions according to the invention can also containthickening agents in order to improve the tactile properties of theemulsion.

In particular, the Pickering emulsions according to the invention canalso contain antioxidants. According to the invention, all antioxidantssuitable or customary for cosmetic and/or dermatological applicationscan be used as favourable antioxidants.

Advantageously, the antioxidants are selected from the group consistingof amino acids (e.g. glycine, histidine, tyrosine, tryptophan) and theirderivatives, imidazoles (e.g. urocanic acid) and their derivatives,peptides, such as D,L-carnosine, D-carnosine, L-carnosine and theirderivatives (e.g. anserine), carotenoids, carotenes (e.g. α-carotene,β-carotene, lycopene) and their derivatives, chlorogenic acid and itsderivatives, lipoic acid and its derivatives (e.g. dihydrolipoic acid),aurothioglucose, propylthiouracil and other thiols (e.g. thioredoxin,glutathione, cysteine, cystine, cystamine and their glycosyl, N-acetyl,methyl, ethyl, propyl, amyl, butyl and lauryl, palmitoyl, oleyl,γ-linoleyl, cholesteryl and glyceryl esters) and their salts, dilaurylthiodipropionate, distearyl thiodipropionate, thiodipropionic acid andits derivatives (esters, ethers, peptides, lipids, nucleotides,nucleosides and salts) and also sulphoximine compounds (e.g. buthioninesulphoximine, homocysteine sulphoximine, buthionine sulphone, penta-,hexa- and heptathionine sulphoximine) in very low tolerable doses (e.g.pmol to μmol/kg), furthermore (metal) chelators (e.g. α-hydroxy fattyacids, palmitic acid, phytic acid, lactoferrin), α-hydroxy acids (e.g.citric acid, lactic acid, malic acid), humic acid, bile acid, bileextracts, bilirubin, biliverdin, EDTA, EGTA and their derivatives,unsaturated fatty acids and their derivatives (e.g. γ-linolenic acid,linoleic acid, oleic acid), folic acid and its derivatives, ubiquinoneand ubiquinol and their derivatives, vitamin C and derivatives (e.g.ascorbyl palmitate, Mg ascorbyl phosphate, ascorbyl acetate),tocopherols and derivatives (e.g. vitamin E acetate), vitamin A andderivatives (vitamin A palmitate) and coniferyl benzoate of benzoin,rutic acid and its derivatives, α-glycosylrutin, ferulic acid,furfurylideneglucitol, carnosine, butylhydroxytoluene,butylhydroxyanisole, nordihydroguaiac acid, nordihydroguaiaretic acid,trihydroxybutyrophenone, uric acid and its derivatives, mannose and itsderivatives, zinc and its derivatives (e.g. ZnO, ZnSO₄), selenium andits derivatives (e.g. selenomethionine), stilbene and its derivatives(e.g. stilbene oxide, trans-stilbene oxide), and the derivatives whichare suitable according to the invention (salts, esters, ethers, sugars,nucleotides, nucleosides, peptides and lipids) of these said activecompounds.

The amount of the abovementioned antioxidants (one or more compounds) inthe preparations according to the invention is preferably 0.001 to 30%by weight, particularly preferably 0.05 to 20% by weight, in particular1 to 10% by weight, based on the total weight of the preparation.

If vitamin E and/or its derivatives are the antioxidant(s), it isadvantageous to select their respective concentrations from the range of0.001-10% by weight, based on the total weight of the formulation.

If vitamin A, or vitamin A derivatives, or carotenes or theirderivatives are the antioxidant(s), it is advantageous to select theirrespective concentrations from the range of 0.001-10% by weight, basedon the total weight of the formulation.

Cosmetic and dermatological preparations which are present in the formof a sunscreen composition are also favourable. Preferably, thesecontain at least one UV-A filter substance and/or at least one UV-Bfilter substance and/or at least one further inorganic pigment from thegroup consisting of the oxides of iron, zirconium, silicon, manganese,aluminium, cerium and mixtures thereof and modifications in which theoxides are the active agents.

However, it is also advantageous within the meaning of the presentinvention to make available those cosmetic and dermatologicalpreparations whose main purpose is not protection from sunlight, butwhich nevertheless contain UV protection substances. Thus, UV-A and UV-Bfilter substances are usually incorporated, for example, in day creams.

Advantageously, preparations according to the invention can containsubstances which absorb UV radiation in the UV-B range, the total amountof the filter substances being, for example, 0.1% by weight to 30% byweight, preferably 0.5 to 10% by weight, in particular 1.0 to 6.0% byweight, based on the total weight of the preparations, in order to makeavailable cosmetic preparations which protect the hair or the skin fromthe entire range of ultraviolet radiation.

If the emulsions according to the invention contain UV-B filtersubstances, these can be oil-soluble or water-soluble. Advantageousoil-soluble UV-B filters according to the invention are, for example:

3-benzylidenecamphor derivatives, preferably3-(4-methylbenzylidene)camphor, 3-benzylidenecamphor;

4-aminobenzoic acid derivatives, preferably 2-ethylhexyl4-dimethylaminobenzoate, amyl 4-dimethylaminobenzoate;

esters of cinnamic acid, preferably 2-ethylhexyl 4-methoxycinnamate,isopentyl 4-methoxycinnamate;

esters of salicylic acid, preferably 2-ethylhexyl salicylate,4-isopropylbenzyl salicylate, homomenthyl salicylate,

derivatives of benzophenone, preferably 2-hydroxy-4-methoxybenzophenone,2-hydroxy-4-methoxy-4′-methylbenzophenone,2,2′-dihydroxy-4-methoxybenzo-phenone;

esters of benzalmalonic acid, preferably 2-ethylhexyl4-methoxybenzalmalonate,

triazine derivatives which are symmetrical with respect to the C₃ axisof the triazine parent structure, preferably tris-2-ethylhexyl4,4′,4″-(1,3,5-triazine-2,4,6, -triyltriimino)trisbenzoate,

benzotriazole derivatives, preferably2,2′-methylene-bis(6-(2H-benzotriazol-2-yl)-4-(1,1,3,3,-tetramethylbutyl)phenol)and UV filters bonded to polymers.

Advantageous water-soluble UV-B filters are, for example:

salts of 2-phenylbenzimidazole-5-sulphonic acid such as its sodium salt,potassium salt or its triethanolammonium salt, and the suphonic aciditself;

sulphonic acid derivatives of benzophenones, preferably2-hydroxy-4-methoxybenzophenone-5-sulphonic acid and its salts;

sulphonic acid derivatives of 3-benzylidenecamphor, such as, forexample, 4-(2-oxo-3-bomylidenemethyl)benzenesulphonic acid,2-methyl-5-(2-oxo-3-bornylidenemethyl)sulphonic acid and their salts.

The list of the said UV-B filters which can be used in the Pickeringemulsions according to the invention should, of course, be non-limiting.

It can also be advantageous to use UV-A filters which hitherto havecustomarily been contained in cosmetic preparations in Pickeringemulsions according to the invention. These substances are preferablyderivatives of dibenzoylmethane, in particular1-(4′-tert-butylphenyl)-3-(4′-methoxyphenyl)propane-1,3-dione and1-phenyl-3-(4′-isopropylphenyl)-propane-1,3-dione.

Other advantageous UV-A filter substances arephenylene-1,4-bis(2-benzimidazyl)-3,3′-5,5′-tetrasulphonic acid:

and its salts, particularly the corresponding sodium, potassium ortriethanolammonium salts, in particular the bis-sodium salt ofphenylene-1,4-bis(2-benzimidazyl)-3,3′-5,5′-tetrasulphonic acid:

and 1,4-di(2-oxo-10-sulfo-3-bornylidenemethyl)benzene and salts thereof(particularly the corresponding 10-sulfato compounds, in particular thecorresponding sodium, potassium or triethanolammonium salt), which isalso referred to asbenzene-1,4-di(2-oxo-3-bornylidenemethyl-10-sulphonic acid) and ischaracterized by the following structure:

Preparations which contain UV-A filters are also a subject of theinvention. The amounts used for the UV-B combination can be employed.

Preparations according to the invention can also be advantageously usedas bases for cosmetic deodorants and antiperspirants, so that aparticular embodiment of the present invention relates to Pickeringemulsions as bases for cosmetic deodorants.

Cosmetic deodorants are used to control body odour which arises whenfresh perspiration, which is in itself odourless, is decomposed bymicroorganisms. Customary cosmetic deodorants are based on various modesof action.

In antiperspirants, astringents, mainly aluminium salts, such asaluminium hydroxychloride (aluminium chlorohydrate), reduce theformation of perspiration.

The use of antimicrobial substances in cosmetic deodorants can reducethe bacterial flora of the skin. In an ideal situation, only themicroorganisms which cause the odour should be effectively reduced, Theflow of perspiration itself is not influenced as a result, and in idealcircumstances, only microbial decomposition of perspiration is stoppedtemporarily.

The combination of astringents and antimicrobial active substances inone and the same composition is also common.

All active ingredients common for deodorants or antiperspirants canadvantageously be used, for example odour concealers, such as customaryperfume constituents, odour absorbers, for example the phyllosilicatesdescribed in Laid-open Patent Specification DE 40 09 347, of these inparticular montmorillonite, kaolinite, illite, beidellite, nontronite,saponite, hectorite, bentonite, smectite, and also, for example, zincsalts of ricinoleic acid. Antibacterial agents are also suitable to beincorporated into the novel W/O emulsion sticks. Advantageous substancesare, for example, 2,4,4′-trichloro-2′-hydroxy diphenyl ether (Irgasan),1,6-di(4-chlorophenylbiguanido)hexane (chlorhexidine),3,4,4′-trichlorocarbanilide, quaternary ammonium compounds, oil ofcloves, mint oil, thyme oil, triethyl citrate, farnesol(3,7,11-trimethyl-2,6,10-dodecatrien-1-ol) and also the activeingredients or active ingredient combinations described in the Laid-openPatent Specifications DE-A-37 40 186, DE-A-39 38 140, DE-A-42 04 321,DE-A-42 29 707, DE-A-43 09 372, DE-A44 11 664, DE-A-195 41 967, DE-A-19543 695, DE-A-195 43 696, DE-A-195 47 160, DE-A-196 02 108, DE-A-196 02110, DE-A-196 02 111, DE-A-196 31 003, DE-A-196 31 004 and DE-A-196 34019, and the Patent SSpecifications DE-42 29 737, DE-42 37 081, DE-43 24219, DE-44 29 467, DE-44 23 410 and DE-195 16 705. Sodiumhydrogencarbonate can also be used advantageously.

The list of specified active ingredients and active ingredientcombinations is of course not intended to be limiting.

The amount of antiperspirant active ingredients or deodorants (one ormore compounds) in the preparations is preferably from 0.01 to 30% byweight, particularly preferably from 0.1 to 20% by weight, in particular1-10% by weight, based on the total weight of the preparation.

The examples below serve to illustrate the present invention withoutlimiting it. The numerical values in the examples are percentages byweight, based on the total weight of the respective preparations.

EXAMPLES

1 2 3 4 5 6 W/O W/O W/O O/W O/W O/W Titanium dioxide (Eusolex 2 4 6 3 52 T2000) Zinc oxide 5 4 4 Titanium dioxide (Titandioxid 2 T805) Silica(Aerosil R972) 1 0.5 Talc (Talkum Micron) 0.5 Boron nitride 2 Sodiummaize starch 0.5 1 n-octenylsuccinate Hydroxystearyl hydroxy- 2 2stearate (Elfacos C26) C₂₀₋₄₀-alkyl stearate 1 1 (Kesterwachs K82)C₁₆₋₃₈-alkylhydroxystearolyl 2 3 stearate (Kesterwachs K80P) Behenoxydimethicone (Abil 5 5 Wax 2440) Polyisobutene (Rewopal PIB 5 1000)Caprylic/capric triglyceride 5 5 5 20 20 20 Octyldodecanol 5 5 15 15Mineral oil 10 10 20 Butylene glycol 10 10 20 7 caprylate/caprateC₁₂₋₁₅-alkyl benzoate 10 10 10 5 15 Dimethicone 2 3 Dicaprylyl ether(Cetiol OE) 5 Hydrogenated polyisobutene 2 (Polysynlan)Methylbenzylidenecamphor 3 4 Octyltriazone 1 4 Dibenzoylmethane 2 2Dioctylbutamidotriazone 2 (UVASORB HEB) Preservative 0.5 0.5 0.5 0.5 0.50.5 Glycerol 5 10 3 5 5 5 Biosaccharide gel (Fucogel 5 1000) Hyaluronicacid 0.5 NaCl 1 1 0.5 0.5 MgSO₄ 0.5 Phenylbenzimidazolesul- 1 2 phonicacid Carbomer (Carbopol 981) 0.1 Xanthan gum 0.3 Cellulose gum (NatrosolPlus 0.05 330 CS) NaOH 45% strength solution 0.3 0.1 0.7 in water EDTAsolution 1 1 Water ad ad ad ad ad ad 100 100 100 100 100 100

We claim:
 1. A Pickering emulsion, said Pickering emulsion being afinely dispersed water-in-oil or oil-in-water, said Pickering emulsioncomprising a) an oil phase; b) an aqueous phase, c) microfine particles,said microfine particles: i) having an average particle size of lessthan 200 mm; ii) being dispersible both in water and oil; iii) havingboth hydrophilic and lipophilic properties resulting in amphiphiliccharacter, and iv) which are selected from the group consisting of metaloxides which are coated on the surface thereof with: (A) adimethylpolysiloxane and/or silica gel; and (B) aluminium hydroxideand/or alumina and/or silicon dioxide; d) at least one electrolyte; andat most 0.5% by weight of one or more emulsifiers.
 2. Pickering emulsionaccording to claim 1, wherein said Pickering emulsions are of thewater-in-oil system.
 3. Pickering emulsion according to claim 1, whereinsaid emulsions are emulsifier-free.
 4. Pickering emulsion according toclaim 1, wherein the content of the particles used is between 0.1% byweight and 30% by weight, based on the total weight of the Pickeringemulsion.
 5. Pickering emulsion according to claim 1, wherein theparticles used have been surface-treated to repel water, where theamphiphilic character of the particles is formed or retained. 6.Water-in-oil Pickering emulsion according to claim 1, wherein the totalamount of one or more electrolytes in the emulsion is less than 5.0% byweight, based on the total weight of the Pickering emulsion. 7.Pickering emulsion according to claim 1, wherein the electrolyte isselected from the group consisting of potassium chloride, sodiumchloride, magnesium sulphate, zinc sulphate and mixtures thereof. 8.Pickering emulsions according to claim 1, wherein the electrolyte isselected from the group consisting of electrolytes which are formed fromwater-soluble UV filter substances which carry one or more sulphonicacid groups or sulphonate groups in their molecular structure, and theirsalts.
 9. Pickering emulsion according to claim 1, wherein saidemulsions comprise auxiliaries which contribute to reducing orpreventing a dull or dry feel on the skin following their application.10. A method of caring for skin, said method comprising applying toskin—Pickering emulsion according to any one of claims 2-4, 5‥9 and 1.11. A method of stabilizing a cosmetic or dermatological Pickeringemulsion, which comprising of: a) an oil phase; b) an aqueous phase, c)microfine particles, said microfine particles: i) having an averageparticle size of less than 200 nm; ii) being dispersible both in waterand oil; iii) having both hydrophilic and lipophilic propertiesresulting in amphiphilic character; and iv) which are selected from thegroup consisting of metal oxides which are coated on the surface thereofwith: (A) a dimethylpolysiloxane and/or silica gel; and (B) aluminiumhydroxide and/or alumina and/or silicon dioxide; and at most 0.5% byweight of one or more emulsifiers; which comprises of adding to saidPickering emulsion at least one electrolyte.